Coating compositions with high scratch resistance and weathering stability

ABSTRACT

Disclosed are coating compositions comprising (a) at least one hydroxyl-containing compound (A), (b) at least one compound (B) having free and/or blocked isocyanate groups, and (c) at least one catalyst (D) for the crosslinking of silane groups, where (i) one or more constituents of the coating composition contain hydrolyzable silane groups and (iii) the coating composition can be finally cured to a coating which has statistically distributed regions of an Si—O—Si network. The finally cured coating obtained from the coating composition has a post-crosslinking index (PCI) of less than 2, wherein (PCI) is defined as the ratio of the storage modulus E′(200) at 200° C. to the minimum of the storage modulus E′(min) at a temperature above the measured glass transition temperature Tg.

The present invention relates to thermally curable coating compositions, based on aprotic solvents and comprising polyols and polyisocyanates with hydrolyzable silane groups which lead to coatings which combine a high scratch resistance with high gloss and high weathering stability.

WO-A-01/98393 describes 2K (2-component) coating compositions comprising a polyol binder component and a polyisocyanate crosslinker component partly functionalized with alkoxysilyl groups. These coating compositions are used as primers and are optimized for adhesion to metallic substrates, especially aluminum substrates. Over these coating compositions, as part of an OEM finish or a refinish, it is possible to apply basecoat/clearcoat systems. In terms of scratch resistance and weathering stability, the coating compositions of WO 01/98393 are not optimized.

EP-A-0 994 117 describes moisture-curable mixtures comprising a polyol component and a polyisocyanate component which may partly have been reacted with a monoalkoxysilylalkylamine that has undergone reaction preferably to an aspartate. Although coatings formed from such mixtures do have a certain hardness, they are nevertheless of only limited suitability for OEM applications in terms of their weathering stability and, in particular, their scratch resistance.

US-A-2006/0217472 describes coating compositions which can comprise a hydroxy-functional acrylate, a low molecular mass polyol component, a polyisocyanate, and an amino-functional alkoxysilyl component, preferably bisalkoxysilylamine. Such coating compositions are used as clearcoat material in basecoat/clearcoat systems and lead to scratchproof coatings. Coating compositions of this kind, however, have only very limited storage qualities, and the resulting coatings have low weathering stability, particularly with respect to UV radiation in a wet/dry cycle.

WO 2006/042585 describes clearcoat materials which are suitable for OEM finishing and which as their main binder component comprise polyisocyanates whose isocyanate groups, preferably to an extent of more than 90 mol %, have undergone reaction with bisalkoxysilylamines. Clearcoat materials of this kind combine excellent scratch resistance with high chemical and weathering resistance. But there is still a need for a further improvement in the weathering stability, particularly with respect to cracking under UV irradiation in a wet/dry cycle, with retention of the high level of scratchproofing.

EP-A-1 273 640 describes 2K coating compositions composed of a polyol component and of a crosslinker component consisting of aliphatic and/or cycloaliphatic polyisocyanates, 0.1 to 95 mol % of the free isocyanate groups originally present having undergone reaction with bisalkoxysilylamine. These coating compositions can be used for OEM finishing and, after their curing is complete, combine good scratch resistance with effective resistance to environmental influences. Nevertheless, these coating compositions have a particularly strong propensity toward post-crosslinking, which—straight after final thermal curing—results in only inadequate scratch resistance of the coatings. The strong post-crosslinking also has a negative impact particularly on the weathering stability as it entails an increased risk of tearing under tension.

In the as yet unpublished German patent application P102007013242 there are coating compositions described which comprise surface-actively modified, silane-containing compounds. These coating compositions lead to finally cured coatings which in the near-surface coating zone—owing to the accumulation of the surface-actively modified, silane-containing compounds prior to thermal cure—have a higher density of Si atoms of the Si—O—Si network than in the bulk. This accumulation of the Si—O—Si network at the surface, in contrast, is specifically not exhibited by the coatings of the invention; instead, the regions of the Si—O—Si network of the finally cured coating of the invention are distributed statistically.

Problem and Solution

It was an object of the present invention to provide coating compositions, particularly for the clearcoat film in OEM finishes and automotive refinishes, that lead to a network with a high degree of weathering stability, the unwanted formation of moieties unstable to hydrolysis and weathering being very largely suppressed, in order to ensure high acid resistance. In addition, the coating compositions ought to lead to coatings which already have a high degree of scratchproofing straight after thermal curing and in particular a high retention of gloss after scratch exposure. Moreover, the coatings and coating systems, especially the clearcoat systems, ought to be able to be produced even in film thicknesses>40 μm without stress cracks occurring. This is a key requirement for the use of the coatings and coating systems, particularly of the clearcoat systems, in the technologically and esthetically particularly demanding field of automotive OEM finishing.

The intention in particular was to provide clearcoat systems featuring high resistance, particularly to cracking, under weathering with UV radiation in a wet/dry cycle, in combination with outstanding scratch proofing.

Furthermore, the new coating compositions ought to be preparable easily and with very good reproducibility, and ought not to present any environmental problems during application of the coating material.

Solution to the Problem

In the light of the above objectives, coating compositions have been found comprising

-   -   (a) at least one hydroxyl-containing compound (A),     -   (b) at least one compound (B) having free and/or blocked         isocyanate groups,     -   (c) at least one catalyst (D) for the crosslinking of silane         groups,

where

-   -   (i) one or more constituents of the coating composition contain         hydrolyzable silane groups and     -   (ii) the coating composition can be finally cured to a coating         which has statistically distributed regions of an Si—O—Si         network,

wherein the finally cured coating obtained from the coating composition has a post-crosslinking index (PCI) of less than 2, where

-   -   the post-crosslinking index (PCI) is defined as the ratio of the         storage modulus E′(200) of the finally cured coating, measured         at 200° C., to the minimum of the storage modulus E′(min) of the         finally cured coating, measured at a temperature above the         measured glass transition temperature Tg,     -   the storage moduli E′(200) and E′(min) and also the glass         transition temperature Tg having been measured on free films         with a thickness of 40 μm±10 μm by dynamic-mechanical         thermo-analysis (DMTA) at a heating rate of 2 K per minute and         at a frequency of 1 Hz, and     -   the DMTA measurements on free films with a thickness of 40 μm±10         μm which have been cured for 20 minutes at an article         temperature of 140° C. and stored at 25° C. for 8 days after         curing were carried out before the DMTA measurements.

In light of the prior art it was surprising and unforeseeable for the skilled worker that the objects on which the present invention was based could be achieved by means of the coating composition of the invention.

The components of the invention can be prepared particularly easily and with very good reproducibility, and do not cause any significant toxicological or environmental problems during application of the coating material.

The coating compositions of the invention produce new coatings and coating systems, especially clearcoat systems, which are highly scratchproof and, in contrast to common, highly crosslinked scratchproof systems, are acid-resistant. Moreover, the coatings and coating systems of the invention, especially the clearcoat systems, can be produced even in film thicknesses>40 μm without stress cracks occurring. Consequently the coatings and coating systems of the invention, especially the clearcoat systems, can be used in the technologically and esthetically particularly demanding field of automotive OEM finishing. In that context they are distinguished by particularly high carwash resistance and scratchproofing. The high scratch resistance straight after the final curing of the coatings is given such that the coatings can be handled without problems straight after the final curing. In addition, the resistance of the coatings of the invention to cracking under UV radiation and wet/dry cycling in the CAM180 test (to DIN EN ISO 11341 February 98 and DIN EN ISO 4892-2 November 00), in combination with a high scratch resistance, is outstanding.

DESCRIPTION OF THE INVENTION

The Post-Crosslinking Index (PCI)

In order to achieve the coatings with the requisite high scratch resistance—even directly after thermal curing—in conjunction with good weathering stability it is essential to the invention that the coating compositions cure as far as possible under the applied curing conditions, in other words exhibit low post-crosslinking after the coating has been cured. This low post-crosslinking is expressed through the post-crosslinking index (PCI).

The post-crosslinking index (PCI) is defined as the ratio of the storage modulus E′(200) of the finally cured coating, measured at 200° C., to the minimum of the storage modulus E′(min) of the finally cured coating, measured at a temperature directly above the measured glass transition temperature Tg, i.e., E′(min) is the minimum of the storage modulus which occurs during the DMTA measurement when the measuring temperature is greater than Tg and less than 200° C. By finally cured coating is meant a coating which is cured for 20 minutes at an article temperature of 140° C. and stored at 25° C. for 8 days after curing before the DMTA measurements are carried out. It will be appreciated that the coating compositions of the invention can also be cured under other conditions, differing in accordance with the intended use. Furthermore, it will be appreciated that the coating compositions of the invention can also be stored for less than 8 days after final curing before the storage moduli are measured. Naturally, in that case, generally speaking, the post-crosslinking index in the case of shorter storage of, say, just 1 day at 25° C. will be somewhat higher than in the case of storage at 25° C. for 8 days. To determine the post-crosslinking index by means of DMTA measurements with the objective of ascertaining whether the coating compositions in question are in accordance with the invention, however, it is necessary to cure and store the coating under the reproducible, precisely specified conditions.

The storage moduli E′(200) and E′(min) and also the glass transition temperature Tg, which are required for the determination of the post-crosslinking index, are measured by dynamic-mechanical thermo-analysis (DMTA) at a heating rate of 2 K/min and at a frequency of 1 Hz.

Dynamic-mechanical thermo-analysis is a widely known measurement method for determining the viscoelastic properties of coatings and is described for example in Murayama, T., Dynamic Mechanical Analysis of Polymeric Material, Elsevier, N.Y., 1978 and Loren W. Hill, Journal of Coatings Technology, vol. 64, no. 808, May 1992, pages 31 to 33.

The measurements can be carried out, for example, using the DMTA V instrument from Rheometrics Scientific at a frequency of 1 Hz and an amplitude of 0.2%. The heating rate is 2 K per minute.

The DMTA measurements are carried out on free films with a thickness of 40 μm±10 μm. For this purpose the coating composition of the invention is applied to substrates to which the coating obtained does not adhere. Examples of suitable substrates include glass, Teflon, polyethylene terephthalate and polypropylene. The resulting coating is cured for 20 minutes at an article temperature of 140° C. and stored at 25° C. for 8 days after curing, before the DMTA measurements are carried out.

A further feature of the coating compositions of the invention is that they can be finally cured to a coating which has statistically distributed regions of the Si—O—Si network. This means that there is no deliberate accumulation or depletion of the Si—O—Si network in particular regions of the coating, including, in other words, the near-surface coating zone accumulation that is described in the as yet unpublished German patent application P102007013242.

It is essential to the invention that the finally cured coating obtained from the coating composition has a post-crosslinking index (PCI) of less than 2, preferably of less than or equal to 1.8, more preferably less than or equal to 1.7, and very preferably less than or equal to 1.5.

In this context it is first noted that, generally speaking, the smaller the fraction of silane crosslinking as a proportion of the crosslinking overall, the smaller the post-crosslinking and hence the smaller the post-crosslinking index (PCI). At the same time, however, as the proportion of silane crosslinking goes down, there is also a decrease in the scratch resistance, with the consequence that, for the purpose of achieving the desired very high scratch resistance, a relatively high proportion of silane crosslinking is desired.

The low post-crosslinking index (PCI) to be set in accordance with the invention, of less than 2, preferably less than or equal to 1.8, more preferably less than or equal to 1.7, and very preferably less than or equal to 1.5, can be set by means of a multiplicity of measures, which are elucidated in more detail below. Hence it is possible in accordance with the invention to provide coating compositions having the high proportions of silane crosslinking that are needed for setting a very high scratch resistance, which, owing to the low degree of post-crosslinking (measured by way of the post-crosslinking index), do not have the disadvantages typically associated with high proportions of silane crosslinking. More particularly it is possible, through the setting of the low post-crosslinking index, to provide coating compositions which have a high scratch resistance directly after the final thermal curing of the coating and at the same time exhibit good weathering resistance. Furthermore, the coating compositions of the invention are distinguished at the same time by very good resistance properties on the part of the coatings of the invention with respect to cracking under UV radiation and wet/dry cycling in the CAM180 test (to DIN EN ISO 11341 February 98 and DIN EN ISO 4892-2 November 00), a high gloss, and high gloss retention after weathering.

The Catalyst (D) for the Crosslinking of the Silane Groups

One preferred measure for controlling the post-crosslinking index (PCI) is the catalyst (D) for the crosslinking of the silane groups. As catalyst for the crosslinking of the silane groups and/or the alkoxysilyl units and also for the reaction between the hydroxyl groups of the compound (A) and the free isocyanate groups of the compound (B) it is possible to use compounds that are known per se, if at the same time the low post-crosslinking index is ensured by virtue of the other measures specified further below. Examples of such known catalysts are Lewis acids (electron deficiency compounds), such as, for example, tin naphthenate, tin benzoate, tin octoate, tin butyrate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin oxide, lead octoate, and also catalysts as described in WO-A-2006/042585.

In order to set a low post-crosslinking index, however, it is preferred as catalyst (D) to employ phosphorus-containing, more particularly phosphorus- and nitrogen-containing, catalysts. In this context it is also possible to use mixtures of two or more different catalysts (D).

Examples of suitable phosphorus-containing catalysts (D) are substituted phosphonic diesters and diphosphonic diesters, preferably from the group consisting of acyclic phosphonic diesters, cyclic phosphonic diesters, acyclic diphosphonic diesters and cyclic diphosphonic diesters. Catalysts of this kind are described for example in German patent application DE-A-102005045228.

More particularly, however, use is made as catalyst of substituted phosphoric monoesters and phosphoric diesters, preferably from the group consisting of acylic phosphoric diesters and cyclic phosphoric diesters, more preferably amine adducts of the phosphoric acid monoesters and diesters.

The acyclic phosphoric diesters (D) are selected more particularly from the group consisting of acyclic phosphoric diesters (D) of the general formula (IV):

where the radicals R₁₀ and R₁₁ are selected from the group consisting of:

substituted and unsubstituted alkyl having 1 to 20, preferably 2 to 16, and more particularly 2 to 10 carbon atoms, cycloalkyl having 3 to 20, preferably 3 to 16, and more particularly 3 to 10 carbon atoms, and aryl having 5 to 20, preferably 6 to 14, and more particularly 6 to 10 carbon atoms,

substituted and unsubstituted alkylaryl, arylalkyl, alkylcycloalkyl, cycloalkylalkyl, arylcycloalkyl, cycloalkylaryl, alkylcycloalkylaryl, alkylarylcycloalkyl, arylcycloalkylalkyl, arylalkylcycloalkyl, cycloalkylalkylaryl, and cycloalkylarylalkyl, the alkyl, cycloalkyl, and aryl groups present therein each containing the aforementioned number of carbon atoms, and

substituted or unsubstituted radical of the aforementioned kind, containing at least one, more particularly one, heteroatom selected from the group consisting of oxygen atom, sulfur atom, nitrogen atom, phosphorus atom, and silicon atom, more particularly oxygen atom, sulfur atom and nitrogen atom,

and being able additionally to be hydrogen as well (partial esterification).

With very particular preference use is made as catalyst (D) of the corresponding amine-blocked phosphoric esters, and more particularly here amine-blocked phosphoric acid ethylhexyl esters and amine-blocked phosphoric acid phenyl esters, especially amine-blocked bis(2-ethylhexyl)phosphate.

Examples of amines with which the phosphoric esters are blocked are, more particularly, tertiary amines, an example being triethylamine. For blocking the phosphoric esters it is particularly preferred to use tertiary amines, which ensure high efficacy of the catalyst under the curing conditions of 140° C.

Certain amine-blocked phosphoric acid catalysts are also available commercially (e.g., Nacure products from King Industries). Mention may be made for example of Nacure 4167 from King Industries as a particularly suitable catalyst on the basis of an amine-blocked phosphoric acid partial ester.

The catalysts are used preferably in fractions of 0.01% to 20% by weight, more preferably in fractions of 0.1% to 10% by weight, based on the nonvolatile constituents of the coating composition of the invention. The amount of catalyst used also has a certain influence on the post-crosslinking index, since a relatively low catalyst efficacy can be compensated in part by correspondingly higher amounts employed.

The Structural Units with Hydrolyzable Silane Groups

It is essential to the invention that one or more constituents of the coating composition comprise hydrolyzable silane groups. These hydrolyzable silane groups lead to the construction of the Si—O—Si network which is distributed statistically in the finally cured coating.

Suitable more particularly here are coating compositions in which one or more constituents of the coating composition contain at least partly one or more identical or different structural units of the formula (I)

—X—Si—R″_(x)G_(3-x)   (I)

where

G=identical or different hydrolyzable groups,

X=organic radical, more particularly linear and/or branched alkylene or cycloalkylene radical having 1 to 20 carbon atoms, very preferably X=alkylene radical having 1 to 4 carbon atoms,

R″=alkyl, cycloalkyl, aryl or aralkyl, it being possible for the carbon chain to be interrupted by nonadjacent oxygen, sulfur or NRa groups, with Ra=alkyl, cycloalkyl, aryl or aralkyl, preferably R″=alkyl radical, more particularly having 1 to 6 C atoms,

x=0 to 2, preferably 0 to 1, more preferably x=0.

The structure of these silane radicals also has an influence on the reactivity and hence also on the maximally extensive reaction during the curing of the coating, in other words on the setting of a maximally low post-crosslinking index (PCI).

In terms of the compatibility and the reactivity of the silanes, preference is given to using silanes having 3 hydrolyzable groups, i.e., x=0.

The hydrolyzable groups G may be selected from the group of halogens, more particularly chlorine and bromine, from the group of alkoxy groups, from the group of alkylcarbonyl groups, and from the group of acyloxy groups. Particular preference is given to alkoxy groups (OR′).

The alkoxy radicals (OR′) that are preferred in each case may be alike or different; critical for the structure of the radicals, however, is the extent to which they influence the reactivity of the hydrolyzable silane groups. Preferably R′ is an alkyl radical, more particularly having 1 to 6 C atoms. Particular preference is given to radicals R′ which increase the reactivity of the silane groups, i.e., which represent good leaving groups. With that aim in mind, a methoxy radical is preferred over an ethoxy radical, which is preferred in turn over a propoxy radical. With particular preference, therefore, R′=ethyl and/or methyl, more particularly methyl.

Furthermore, the reactivity of organofunctional silanes may also be influenced considerably by the length of the spacers X between silane functionality and organic functional group that serves for reaction with the modifying constituent. As examples of this, mention may be made of the “alpha” silanes available from Wacker, in which a methylene group is between the Si atom and the functional group, rather than the propylene group that is present in the case of “gamma” silanes. For illustration it is stated that methacryloyloxymethyltrimethoxysilane (“alpha” silane, e.g., commercial product Geniosil® XL 33 from Wacker) is used with preference over methacryloyloxypropyltrimethoxysilane (“gamma” silane, e.g., commercial product Geniosil® GF 31 from Wacker) in order to introduce the hydrolyzable silane groups into the coating composition.

In very general terms, spacers which increase the reactivity of the silanes are preferred over spacers which reduce the reactivity of the silanes.

In addition, the functionality of the silanes also has an effect on the post-crosslinking index. By functionality in this context is meant the number of radicals of the formula (I) per molecule. A monofunctional silane is therefore a silane of the kind which for each silane molecule introduces one radical of the formula (I) into the constituent that is to be modified. A difunctional silane is a silane of the kind which for each silane molecule introduces in each case two radicals of the formula (I) into the constituent.

Particular preference is given in accordance with the invention to coating compositions in which the constituents have been modified with a mixture of a monofunctional silane and a difunctional silane. Difunctional silanes used are more particularly the amino-functional disilanes of the formula (IIa) that are described further below, and monofunctional silanes used are the silanes of the formula (IIIa) that are described further below.

In general, then, for a given level of silanization, the post-crosslinking index (PCI) decreases as the proportion of monofunctional silane goes up, but at the same time there is also a decrease in the scratch resistance. Generally speaking, moreover, as the proportion of difunctional silane goes up, there is an increase in the post-crosslinking index (PCI), but at the same time there is also an increase in the scratch resistance. With high proportions of difunctional silane, therefore, correspondingly different measures must be taken in order to reduce the post-crosslinking index in order to provide the coating compositions of the invention. By way of example, the degree of silanization overall can be lowered; in other words, in the case of the below-described modification of the polyisocyanate component (B) with a (bis-silyl)amine of the formula (IIa), the fraction of isocyanate groups reacted overall with a silane can be chosen to be correspondingly low. Moreover, as the degree of silanization goes up (i.e., as the overall proportion of the isocyanate groups reacted with the compounds (IIa) and (IIIa) goes up) and as the proportion of difunctional silane (IIa) goes up, the influence of the catalyst on the post-crosslinking index becomes increasingly great, with the consequence that, in that case, it is preferred to employ phosphorus-containing catalysts, and more particularly amine-blocked phosphoric acid-based catalysts.

Finally, it is also possible for nonfunctional substituents on the organofunctional silane that is used to introduce the structural units (I) and/or (II) and/or (III) to influence the reactivity of the hydrolyzable silane group. This may be illustrated by way of example taking as an example bulky, voluminous substituents on the amine function, which can reduce the reactivity of amine-functional silanes. Against this background, N-(n-butyl)-3-aminopropyltrimethoxysilane is preferred over N-cyclo-hexyl-3-aminopropyltrimethoxysilane for the introduction of the structural units (III).

Very generally, the radicals which increase the reactivity of the silanes are preferred over radicals which lower the reactivity of the silanes.

There are different ways in which the structural units of the formula (I) can be introduced into the constituents of the coating composition. Common to the various ways, however, is that the introduction of the structural units takes place via a reaction of the functional groups of the constituents to be modified with complementary functional groups of the silane. Set out below by way of example, therefore, are various possibilities for the introduction of the structural units (I) into the hydroxyl-containing compound (A)—which, where appropriate, also contains further reactive groups—and/or into the compound (B) containing isocyanate groups.

Use is made, more particularly in the context of Michael additions, of, for example, primary aminosilanes, such as 3-aminopropyltriethoxysilane (available for example under the trade name Geniosil® GF 93 from Wacker Chemie), 3-aminopropyltrimethoxysilane (available for example under the trade name Geniosil® GF 96 from Wacker Chemie), N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (available for example under the trade name Geniosil® GF 9 and also Geniosil® GF 91 from Wacker Chemie), N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane (available for example under the trade name Geniosil® GF 95 from Wacker Chemie), and the like.

Use is made, more particularly in the context of additions to isocyanate-functional compounds, of, for example, secondary aminosilanes, such as, for example, bis(2-trimethoxysilylethyl)amine, bis(2-triethoxysilylethyl)amine, bis(3-triethoxysilylpropyl)amine (available under the trade name Dynasylan® 1122 from Degussa), bis(3-trimethoxysilylpropyl)amine (available under the trade name Dynasylan® 1124 from Degussa), bis(4-triethoxysilylbutyl)amine, N-(n-butyl)-3-aminopropyltrimethoxysilane (available under the trade name Dynasylan® 1189 from Degussa), N-(n-butyl)-3-aminopropyltriethoxysilane, N-cyclohexyl-3-aminopropyltrimethoxysilane (available under the trade name Geniosil® GF 92 from Wacker Chemie), N-cyclohexyl-3-aminopropyltriethoxysilane, N-cyclohexylaminomethylmethyldiethoxysilane (available from Wacker Chemie under the trade name Geniosil® XL 924), N-cyclohexylaminomethyltriethoxysilane (available from Wacker Chemie under the trade name Geniosil XL 926), N-phenylaminomethyltrimethoxysilane (available from Wacker Chemie under the trade name Geniosil XL 973), and the like.

Epoxy-functional silanes can be used more particularly for addition to compounds with carboxylic acid or anhydride functionality. Examples of suitable epoxy-functional silanes are 3-glycidyloxypropyltrimethoxysilane (available from Degussa under the trade name Dynasylan® GLYMO), 3-glycidyloxypropyltriethoxysilane (available from Degussa under the trade name Dynasylan® GLYEO), and the like.

Anhydride-functional silanes can be used more particularly for addition to epoxy-functional compounds. An example that may be mentioned of a silane with anhydride functionality is 3-(triethoxysilyl)propylsuccinic anhydride (available from Wacker Chemie under the trade name Geniosil® GF 20).

Silanes of this kind can be used in the context of Michael reactions or else in the context of metal-catalyzed reactions. Those exemplified are 3-methacryloyloxypropyltrimethoxysilane (available for example from Degussa under the trade name Dynasilan® MEMO, or from Wacker Chemie under the trade name Geniosil® GF 31), 3-methacryloyloxypropyltriethoxysilane, vinyltrimethoxysilane (available, among others, from Wacker Chemie under the trade name Geniosil® XL 10), vinyldimethoxymethylsilane (available, among others, from Wacker Chemie under the trade name Geniosil® XL 12), vinyltriethoxysilane (available, among others, from Wacker Chemie under the trade name Geniosil® GF 56), (methacryloyloxymethyl)methyldimethoxysilane (available, among others, from Wacker Chemie under the trade name Geniosil® XL 32), methacryloyloxymethyltrimethoxysilane (available, among others, from Wacker Chemie under the trade name Geniosil® XL 33), (methacryloyloxymethyl)methyldiethoxysilane (available, among others, from Wacker Chemie under the trade name Geniosil® XL 34), methacryloyloxymethyltriethoxysilane (available, among others, from Wacker Chemie under the trade name Geniosil® XL 36).

Silanes with isocyanato function or carbamate function are employed in particular in the context of reactions with hydroxy-functional compounds. Examples of silanes with isocyanato function are described in WO 07/03857, for example.

Examples of suitable isocyanatoalkyltrialkoxysilanes are isocyanatopropyltrimethoxysilane, isocyanatopropylmethyldimethoxysilane, isocyanatopropylmethyldiethoxysilane, isocyanatopropyltriethoxysilane, isocyanatopropyltriisopropoxysilane, isocyanatopropylmethyldiisopropoxysilane, isocyanatoneohexyltrimethoxysilane, isocyanatoneohexyldimethoxysilane, isocyanatoneohexyldiethoxysilane, isocyanatoneohexyltriethoxysilane, isocyanatoneohexyltriisopropoxysilane, isocyanatoneohexyldiisopropoxysilane, isocyanatoisoamyltrimethoxysilane, isocyanatoisoamylmethyldimethoxysilane, isocyanatoisoamylmethyldiethoxysilane, isocyanatoisoamyltriethoxysilane, isocyanatoisoamyltriisopropoxysilane, and isocyanatoisoamylmethyldiisopropoxysilane. Many isocyanatoalkyltri- and -di-alkoxysilanes are available commercially, for example, under the designation SILQUEST® from OSi Specialties, Inc., a Witco Corporation company.

The isocyanatopropylalkoxysilane used preferably has a high degree of purity, more particularly a purity of at least 95%, and is preferably free from additives, such as transesterification catalysts, which can lead to unwanted side reactions.

Use is made more particularly of (isocyanatomethyl)methyldimethoxysilane (available from Wacker Chemie under the trade name Geniosil® XL 42), 3-isocyanatopropyltrimethoxysilane (available from Wacker Chemie under the trade name Geniosil® XL 40), and N-dimethoxy(methyl)silylmethyl O-methylcarbamate (available from Wacker Chemie under the trade name Geniosil® XL 65).

More particular preference in accordance with the invention is given to coating compositions comprising at least one hydroxyl-containing compound (A) and at least one isocyanato-containing compound (B), wherein one or more constituents of the coating composition comprise, as additional functional components, between

2.5 and 97.5 mol %, based on the entirety of structural units (II) and (III), of at least one structural unit of the formula (II)

—N(X—SiR″x(OR′)3-x)n(X′—SiR″y(OR′)3-y)m   (II)

where

R′=hydrogen, alkyl or cycloalkyl, it being possible for the carbon chain to be interrupted by nonadjacent oxygen, sulfur or NRa groups, where Ra=alkyl, cycloalkyl, aryl or aralkyl, preferably R′=ethyl and/or methyl X,X′=linear and/or branched alkylene or cycloalkylene radical having 1 to 20 carbon atoms, preferably X,X′=alkylene radical having 1 to 4 carbon atoms,

R″=alkyl, cycloalkyl, aryl or aralkyl, it being possible for the carbon chain to be interrupted by nonadjacent oxygen, sulfur or NRa groups, where Ra=alkyl, cycloalkyl, aryl or aralkyl, preferably R″=alkyl radical, in particular having 1 to 6 carbon atoms,

n=0 to 2, m=0 to 2, m+n=2, and x,y=0 to 2,

and

between 2.5 and 97.5 mol %, based on the entirety of structural units (II) and (III), of at least one structural unit of the formula (III)

-Z-(X—SiR″x(OR′)3-x)   (III),

where

Z=-NH—, —NR—, —O—, with

R=alkyl, cycloalkyl, aryl or aralkyl, it being possible for the carbon chain to be interrupted by nonadjacent oxygen, sulfur or NRa groups, with Ra=alkyl, cycloalkyl, aryl or aralkyl,

x=0 to 2

X, R′, R″ have the meaning given in formula (II).

Very particular preference is given to coating compositions wherein one or more constituents of the coating composition contain between 5 and 95 mol %, more particularly between 10 and 90 mol %, more preferably between 20 and 80 mol %, and especially between 30 and 70 mol %, based in each case on the entirety of the structural units (II) and (III), of at least one structural unit of the formula (II), and between 5 and 95 mol %, more particularly between 10 and 90 mol %, more preferably between 20 and 80 mol %, and especially between 30 and 70 mol %, based in each case on the entirety of the structural units (II) and (III), of at least one structural unit of the formula (III).

The Hydroxyl-Containing Compound (A)

As hydroxyl-containing compound (A) it is preferred to use both low molecular mass polyols and also oligomeric and/or polymeric polyols.

Low molecular mass polyols used are, for example, diols, such as, preferably, ethylene glycol, neopentyl glycol, 1,2-propanediol, 2,2-dimethyl-1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, and 1,2-cyclohexanedimethanol, and also polyols, such as, preferably, trimethylolethane, trimethylolpropane, trimethylolhexane, 1,2,4-butanetriol, pentaerythritol, and dipentaerythritol. Low molecular mass polyols of this kind are preferably admixed in minor proportions to the oligomeric and/or polymeric polyol component (A).

The preferred oligomeric and/or polymeric polyols (A) have mass-average molecular weights Mw>500 daltons, as measured by means of GPC (gel permeation chromatography), preferably between 800 and 100 000 daltons, in particular between 1000 and 50 000 daltons. Particularly preferred are polyester polyols, polyurethane polyols, polysiloxane polyols, and, in particular, polyacrylate polyols and/or polymethacrylate polyols, and their copolymers, referred to as polyacrylate polyols below. The polyols preferably have an OH number of 30 to 400 mg KOH/g, in particular between 100 and 300 KOH/g. The glass transition temperatures, as measured by DSC (differential thermoanalysis), of the polyols are preferably between −150 and 100° C., more preferably between −120° C. and 80° C.

Suitable polyester polyols are described for example in EP-A-0 994 117 and EP-A-1 273 640. Polyurethane polyols are prepared preferably by reacting polyester polyol prepolymers with suitable di- or polyisocyanates and are described in EP-A-1 273 640, for example. Suitable polysiloxane polyols are described for example in WO-A-01/09260, and the polysiloxane polyols recited therein can be employed preferably in combination with further polyols, especially those having relatively high glass transition temperatures.

The polyacrylate polyols that are very particularly preferred in accordance with the invention are generally copolymers and preferably have mass-average molecular weights Mw of between 1000 and 20 000 daltons, in particular between 1500 and 10 000 daltons, in each case measured by means of gel permeation chromatography (GPC) against a polystyrene standard. The glass transition temperature of the copolymers is generally between −100 and 100° C., in particular between −50 and 80° C. (measured by means of DSC measurements). The polyacrylate polyols preferably have an OH number of 60 to 250 mg KOH/g, in particular between 70 and 200 KOH/g, and an acid number of between 0 and 30 mg KOH/g.

The hydroxyl number (OH number) indicates how many mg of potassium hydroxide are equivalent to the amount of acetic acid bound by 1 g of substance during acetylation. For the determination, the sample is boiled with acetic anhydride-pyridine and the acid formed is titrated with potassium hydroxide solution (DIN 53240-2). The acid number here indicates the number of mg of potassium hydroxide consumed in neutralizing 1 g of the respective compound of component (b) (DIN EN ISO 2114).

The selection of the hydroxyl-containing binders as well may be used to influence the post-crosslinking index. Generally speaking, indeed, as the OH number of component (A) goes up, it is possible to lower the degree of silanization, i.e., the amount of structural units of the formula (I) and/or (II) and/or (III), which in turn results in a lower post-crosslinking index.

Hydroxyl-containing monomer units used are preferably hydroxyalkyl acrylates and/or hydroxyalkyl methacrylates, such as, in particular, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 3-hydroxybutyl acrylate, 3-hydroxybutyl methacrylate, and, in particular, 4-hydroxybutyl acrylate and/or 4-hydroxybutyl methacrylate.

Further monomer units used for the polyacrylate polyols are preferably alkyl methacrylates and/or alkyl methacrylates, such as, preferably, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, amyl acrylate, amyl methacrylate, hexyl acrylate, hexyl methacrylate, ethylhexyl acrylate, ethylhexyl methacrylate, 3,3,5-trimethylhexyl acrylate, 3,3,5-trimethylhexyl methacrylate, stearyl acrylate, stearyl methacrylate, lauryl acrylate or lauryl methacrylate, cycloalkyl acrylates and/or cycloalkyl methacrylates, such as cyclopentyl acrylate, cyclopentyl methacrylate, isobornyl acrylate, isobornyl methacrylate, or, in particular, cyclohexyl acrylate and/or cyclohexyl methacrylate.

Further monomer units which can be used for the polyacrylate polyols are vinylaromatic hydrocarbons, such as vinyltoluene, alpha-methylstyrene or, in particular, styrene, amides or nitriles of acrylic or methacrylic acid, vinyl esters or vinyl ethers, and, in minor amounts, in particular, acrylic and/or methacrylic acid.

In a further embodiment of the invention the hydroxyl-containing compound A, as well as the hydroxyl groups, comprises structural units of the formula (I) and/or of the formula (II) and/or of the formula (III).

Structural units of the formula (II) can be introduced into the compound (A) by incorporation of monomer units containing such structural units, or by reaction of polyols containing further functional groups with a compound of the formula (IIa)

HN(X—SiR″x(OR′)3-x)n(X′—SiR″y(OR′)3-y)m   (IIa),

where the substituents are as defined above. For the reaction of the polyol with the compound (IIa), the polyol, correspondingly, has further functional groups which react with the secondary amino group of the compound (IIa), such as acid or epoxy groups in particular. Inventively preferred compounds (IIa) are bis(2-ethyltrimethoxysilyl)amine, bis(3-propyltrimethoxysilyl)amine, bis(4-butyltrimethoxysilyl)amine, bis(2-ethyltriethoxysilyl)amine, bis(3-propyltriethoxysilyl)amine and/or bis(4-butyltriethoxysilyl)amine. bis(3-Propyltrimethoxysilyl)amine is especially preferred. Aminosilanes of this kind are available for example under the trade name DYNASILAN® from DEGUSSA or Silquest® from OSI.

Monomer units which carry the structural elements (II) are preferably reaction products of acrylic and/or methacrylic acid or of epoxy-functional alkyl acrylates and/or methacrylates with the abovementioned compounds (IIa).

Structural units of the formula (III) can be introduced into the compound (A) by incorporation of monomer units containing such structural units or by reaction of polyols containing further functional groups with a compound of the formula (IIIa)

H-Z-(X—SiR″x(OR′)3-x)   (IIIa),

where the substituents are as defined above. For the reaction of the polyol with the compound (IIIa) the polyol, correspondingly, has further functional groups which react with the functional group -ZH of the compound (IIIa), such as acid, epoxy or ester groups in particular. Inventively preferred compounds (IIIa) are omega-aminoalkyl- or omega-hydroxyalkyltrialkoxysilanes, such as, preferably, 2-aminoethyltrimethoxysilane, 2-aminoethyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 4-aminobutyltrimethoxysilane, 4-aminobutyltriethoxysilane, 2-hydroxyethyltrimethoxysilane, 2-hydroxyethyltriethoxysilane, 3-hydroxypropyltrimethoxysilane, 3-hydroxypropyltriethoxysilane, 4-hydroxybutyltrimethoxysilane, and 4-hydroxybutyltriethoxysilane. Particularly preferred compounds (IIIa) are N-(2-(trimethoxysilyl)ethyl)alkylamines, N-(3-(trimethoxysilyl)propyl)alkylamines, N-(4-(trimethoxysilyl)butyl)alkylamines, N-(2-(triethoxysilyl)ethyl)alkylamines, N-(3-(triethoxysilyl)propyl)alkylamines and/or N-(4-(triethoxysilyl)butyl)alkylamines. N-(3-(Trimethoxysilyl)propyl)butylamine is especially preferred. Aminosilanes of this kind are available for example under the trade name DYNASILAN® from DEGUSSA or Silquest® from OSI.

Monomer units which carry the structural elements (III) are preferably reaction products of acrylic and/or methacrylic acid or of epoxy-functional alkyl acrylates and/or methacrylates, and also, in the case of hydroxy-functional alkoxysilyl compounds, transesterification products of alkyl acrylates and/or methacrylates, especially with the abovementioned hydroxy- and/or amino-functional alkoxysilyl compounds (IIIa).

The Isocyanato-Containing Compounds (B)

As component (B) the coating compositions of the invention comprise one or more compounds having free, i.e., nonblocked, and/or blocked isocyanate groups. Preferably the coating compositions of the invention comprise compounds (B) having free isocyanate groups. The free isocyanate groups of the isocyanate-group-containing compounds B may also, however, be used in blocked form. This is preferably the case when the coating compositions of the invention are employed in the form of one-component systems.

The di- and/or polyisocyanates which serve as parent structures for the isocyanato-containing compounds (B) used with preference in accordance with the invention are preferably conventional substituted or unsubstituted aromatic, aliphatic, cycloaliphatic and/or heterocyclic polyisocyanates. Examples of preferred polyisocyanates are as follows: 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, diphenylmethane 4,4′-diisocyanate, diphenylmethane 2,4′-diisocyanate, p-phenylene diisocyanate, biphenyl diisocyanates, 3,3′-dimethyl-4,4′-diphenylene diisocyanate, tetramethylene 1,4-diisocyanate, hexamethylene 1,6-diisocyanate, 2,2,4-trimethylhexane 1,6-diisocyanate, isophorone diisocyanate, ethylene diisocyanate, 1,12-dodecane diisocyanate, cyclobutane 1,3-diisocyanate, cyclohexane 1,3-diisocyanate, cyclohexane 1,4-diisocyanate, methylcyclohexyl diisocyanates, hexahydrotoluene 2,4-diisocyanate, hexahydrotoluene 2,6-diisocyanate, hexahydrophenylene 1,3-diisocyanate, hexahydrophenylene 1,4-diisocyanate, perhydrodiphenylmethane 2,4′-diisocyanate, 4,4′-methylenedicyclohexyl diisocyanate (e.g., Desmodur® W from Bayer AG), tetramethylxylyl diisocyanates (e.g., TMXDI® from American Cyanamid), and mixtures of the aforementioned polyisocyanates. Additionally preferred polyisocyanates are the biuret dimers and the isocyanurate trimers of the aforementioned diisocyanates.

Particularly preferred polyisocyanates PI are hexamethylene 1,6-diisocyanate, isophorone diisocyanate, and 4,4′-methylenedicyclohexyl diisocyanate, their biuret dimers and/or isocyanurate trimers.

In a further embodiment of the invention the polyisocyanates are polyisocyanate prepolymers containing urethane structural units which are obtained by reacting polyols with a stoichiometric excess of aforementioned polyisocyanates. Polyisocyanate prepolymers of this kind are described for example in U.S. Pat. No. 4,598,131.

The isocyanato-functional compounds (B) that are especially preferred in accordance with the invention, functionalized with the structural units (II) and (III), are prepared with particular preference by reacting the aforementioned di- and/or polyisocyanates with the aforementioned compounds (IIa) and (IIIa), by reacting

between 2.5 and 90 mol %, preferably 5 to 85 mol %, more preferably 7.5 to 80 mol %, of the isocyanate groups in the core polyisocyanate structure with at least one compound (IIa) and

between 2.5 and 90 mol %, preferably 5 to 85 mol %, more preferably 7.5 to 80 mol %, of the isocyanate groups in the core polyisocyanate structure with at least one compound (IIIa).

The total fraction of the isocyanate groups reacted with the compounds (IIa) and (IIIa) in the polyisocyanate compound (B) is between 5 and 95 mol %, preferably between 10 and 90 mol %, more preferably between 15 and 85 mol % of the isocyanate groups in the core polyisocyanate structure. Particularly in the case of a high degree of silanization, i.e., if a high proportion of the isocyanate groups, more particularly at least 50 mol %, has been reacted with the compounds (IIa)/(IIIa), the isocyanate groups are advantageously reacted with a mixture of the compounds (IIa) and (IIIa).

Particularly preferred compounds (IIa) are bis(2-ethyltrimethoxysilyl)amine, bis(3-propyltrimethoxysilyl)amine, bis(4-butyltrimethoxysilyl)amine, bis(2-ethyltriethoxysilyl)amine, bis(3-propyltriethoxysilyl)amine and/or bis(4-butyltriethoxysilyl)amine. bis(3-Propyltrimethoxysilyl)amine is especially preferred. Aminosilanes of this kind are available for example under the trade name DYNASILAN® from DEGUSSA or Silquest® from OSI.

Preferred compounds (IIIa) are 2-aminoethyltrimethoxysilane, 2-aminoethyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 4-aminobutyltrimethoxysilane, 4-aminobutyltriethoxysilane, 2-hydroxyethyltrimethoxysilane, 2-hydroxyethyltriethoxysilane, 3-hydroxypropyltrimethoxysilane, 3-hydroxypropyltriethoxysilane, 4-hydroxybutyltrimethoxysilane, and 4-hydroxybutyltriethoxysilane.

Particularly preferred compounds (IIIa) are N-(2-(trimethoxysilyl)ethyl)alkylamines, N-(3-(trimethoxysilyl)propyl)alkylamines, N-(4-(trimethoxysilyl)butyl)alkylamines, N-(2-(triethoxysilyl)ethyl)alkylamines, N-(3-(triethoxysilyl)propyl)alkylamines and/or N-(4-(triethoxysilyl)butyl)alkylamines. N-(3-(Trimethoxysilyl)propyl)butylamine is especially preferred. Aminosilanes of this kind are available for example under the trade name DYNASILAN® from DEGUSSA or Silquest® from OSI.

Especially preferred isocyanato-containing compounds (B) are reaction products of hexamethylene 1,6-diisocyanate and/or isophorone diisocyanate, and/or their isocyanurate trimers, with bis(3-propyltrimethoxysilyl)amine and N-(3-(trimethoxysilyl)propyl)butylamine. The reaction of the isocyanato-containing compounds (B) with the compounds (IIa) and (IIIa) takes place preferably in inert gas at temperatures of not more than 100° C., preferably at not more than 60° C.

The free isocyanate groups of the isocyanato-containing compounds B can also be used in blocked form. This is preferably the case when the coating compositions of the invention are used as one-component systems. For the purpose of blocking it is possible in principle to use any blocking agent which can be used for blocking polyisocyanates and which has a sufficiently low unblocking temperature. Blocking agents of this kind are very familiar to the skilled worker. It is preferred to use blocking agents as described in EP-A-0 626 888 and EP-A-0 692 007.

The Combination of Components A and B, and Further Components of the Coating Composition

The weight fraction of hydroxyl-containing compounds A to be employed, based on the weight fraction of the isocyanato-containing compounds B, is dependent on the hydroxy equivalent weight of the polyol and on the equivalent weight of the free isocyanate groups of the polyisocyanate B.

It is preferable that in the coating composition of the invention there is one or more constituents between 2.5 to 97.5 mol %, based on the sum of structural units (II) and (III), of at least one structural unit (II) and between 2.5 to 97.5 mol %, based on the sum of structural units (II) and (III), of at least one of structural units (III).

The coating compositions of the invention contain preferably between 2.5% and 97.5%, more preferably between 5% and 95%, very preferably between 10% and 90%, and in particular between 20% and 80%, by weight, based on the amount of nonvolatile substances in the coating composition, of the hydroxyl-containing compounds (A), and preferably between 2.5% and 97.5%, more preferably between 5% and 95%, very preferably between 10% and 90%, and in particular between 20% and 80%, by weight, based on the amount of nonvolatile substances in the coating composition, of the isocyanato-containing compounds (B).

Based on the sum of the functional groups critical for crosslinking in the coating composition of the invention, formed from the fractions of the hydroxyl and isocyanate groups and also the fractions of the structural elements (I) and/or (II) and/or (III), the structural elements (I) and/or (II) and/or (III) are present preferably in fractions of 2.5 to 97.5 mol %, more preferably between 5 and 95 mol %, and very preferably between 10 and 90 mol %.

In order to ensure further-improved, very good resistance properties on the part of the coatings of the invention toward cracking under UV radiation and wet/dry cycling in the CAM180 test (to DIN EN ISO 11341 February 98 and DIN EN ISO 4892-2 November 00) in combination with a high scratch resistance directly following the final thermal cure, a high gloss, and high gloss retention after weathering, it is additionally preferred to choose the level of structural units (I) and/or (II) and/or (III) to be at most such that the coating compositions of the invention in the finally cured state have a storage modulus E′ (200° C.), measured at 200° C. in accordance with the method described above in connection with the description of the PCI, of less than 4*10⁸ Pa, more particularly of less than or equal to 3*10⁸ Pa.

It is particularly preferred, in addition, to select the amount of structural units (I) and/or (II) and/or (III) to be at most such that the coating compositions of the invention contain less than 6.5% by mass of Si of the structural units (I) and/or (II) and/or (III), very preferably not more than 6.0% by mass of Si of the structural units (I) and/or (II) and/or (III), based in each case on the solids content of the coating compositions. The silane content in % by mass of Si is determined arithmetically from the amounts of the compounds with the structural unit (I) and, respectively, the compounds (IIa) and/or (IIIa) that are used.

In a further embodiment of the invention the structural elements (I), (II) and/or (III) may additionally also be part of one or more further components (C), different than the components (A) and (B), in which case the criteria to be applied are those specified above. By way of example it is possible as component (C) to use oligomers or polymers containing alkoxysilyl groups, such as, for example, the poly(meth)acrylates specified in patents and patent applications U.S. Pat. No. 4,499,150, U.S. Pat. No. 4,499,151 or EP-A-0 571 073, as carriers of structural elements (III), or to use the compounds specified in WO-A-2006/042585, as carriers of structural elements (II). Generally speaking, components (C) of this kind are used in fractions of up to 40%, preferably up to 30%, more preferably up to 25%, by weight, based on the nonvolatile constituents of the coating composition. The weight fractions of the polyol A and of the polyisocyanate B are preferably selected such that the molar equivalent ratio of the unreacted isocyanate groups of the isocyanate-containing compounds (B) to the hydroxyl groups of the hydroxyl-containing compounds (A) is between 0.9:1 and 1:1.1, preferably between 0.95:1 and 1.05:1, more preferably between 0.98:1 and 1.02:1.

Where the compositions are one-component coating compositions, a selection is made of the isocyanato-containing compounds (B) whose free isocyanate groups have been blocked with the blocking agents described above.

In the case of the inventively preferred 2-component (2K) coating compositions, a coating component comprising the hydroxyl-containing compound (A) and also further components, described below, is mixed conventionally with a further coating component, comprising the isocyanato-containing compound (B) and, where appropriate, further of the components described below, this mixing taking place shortly before the coating composition is applied; generally speaking, the coating component that comprises the compound (A) comprises the catalyst and also part of the solvent.

Solvents suitable for the coating compositions of the invention are in particular those which, in the coating composition, are chemically inert toward the compounds (A) and (B) and also do not react with (A) and (B) when the coating composition is being cured. Examples of such solvents are aliphatic and/or aromatic hydrocarbons such as toluene, xylene, solvent naphtha, Solvesso 100 or Hydrosol® (from ARAL), ketones, such as acetone, methyl ethyl ketone or methyl amyl ketone, esters, such as ethyl acetate, butyl acetate, pentyl acetate or ethyl ethoxypropionate, ethers, or mixtures of the aforementioned solvents. The aprotic solvents or solvent mixtures preferably have a water content of not more than 1%, more preferably not more than 0.5%, by weight, based on the solvent.

Besides the compounds (A), (B), and (C) it is possible additionally to use further binders (E), which preferably are able to react and form network points with the hydroxyl groups of the compound (A) and/or with the free isocyanate groups of the compound (B) and/or with the alkoxysilyl groups of the compounds (A), (B) and/or (C).

By way of example it is possible to use amino resins and/or epoxy resins as component (E). Suitable amino resins are the typical, known amino resins, some of whose methylol and/or methoxymethyl groups may have been defunctionalized by means of carbamate or allophanate groups. Crosslinking agents of this kind are described in patents U.S. Pat. No. 4,710,542 and EP-B-0 245 700 and also in the article by B. Singh and coworkers, “Carbamylmethylated Melamines, Novel Crosslinkers for the Coatings Industry” in Advanced Organic Coatings Science and Technology Series, 1991, Volume 13, pages 193 to 207.

Generally speaking, such components (E) are used in fractions of up to 40%, preferably up to 30%, more preferably up to 25%, by weight, based on the nonvolatile constituents of the coating composition.

The coating composition of the invention may further comprise at least one typical, known coatings additive in effective amounts, i.e. in amounts preferably up to 30%, more preferably up to 25%, and in particular up to 20% by weight, in each case based on the nonvolatile constituents of the coating composition.

Examples of suitable coatings additives are:

-   -   particularly UV absorbers;     -   particularly light stabilizers such as HALS compounds,         benzotriazoles or oxalanilides;     -   free-radical scavengers;     -   slip additives;     -   polymerization inhibitors;     -   defoamers;     -   reactive diluents, of the kind which are common knowledge from         the prior art, and which are preferably inert toward the         —Si(OR)3 groups;     -   wetting agents such as siloxanes, fluorine compounds, carboxylic         monoesters, phosphoric esters, polyacrylic acids and their         copolymers, or polyurethanes;     -   adhesion promoters such as tricyclodecanedimethanol;     -   flow control agents;     -   film-forming assistants such as cellulose derivatives;     -   fillers such as, for example, nanoparticles based on silicon         dioxide, aluminum oxide or zirconium oxide; for further details         refer to Römpp Lexikon “Lacke und Druckfarben” Georg Thieme         Verlag, Stuttgart, 1998, pages 250 to 252;     -   rheology control additives, such as the additives known from         patents WO 94/22968, EP-A-0 276 501, EP-A-0 249 201 or WO         97/12945; crosslinked polymeric microparticles, as disclosed for         example in EP-A-0 008 127; inorganic phyllosilicates such as         aluminum-magnesium silicates, sodium-magnesium and         sodium-magnesium-fluorine-lithium phyllosilicates of the         montmorillonite type; silicas such as Aerosils; or synthetic         polymers containing ionic and/or associative groups such as         polyvinyl alcohol, poly(meth)acrylamide, poly(meth)acrylic acid,         polyvinylpyrrolidone, styrene-maleic anhydride copolymers or         ethylene-maleic anhydride copolymers and their derivatives, or         hydrophobically modified ethoxylated urethanes or polyacrylates;     -   and/or flame retardants.

In a further embodiment of the invention the coating composition of the invention may additionally comprise further pigments and/or fillers and may serve for producing pigmented topcoats. The pigments and/or fillers employed for this purpose are known to the skilled worker.

Because the coatings of the invention produced from the coating compositions of the invention adhere excellently even to electrocoats, surfacer coats, basecoat systems or typical, known clearcoat systems that have already cured, they are outstandingly suitable not only for use in automotive OEM finishing but also for automotive refinish or for the modular scratchproofing of automobile bodies that have already been painted.

The coating compositions of the invention can be applied by any of the typical application methods, such as spraying, knife coating, spreading, pouring, dipping, impregnating, trickling or rolling, for example. In the course of such application, the substrate to be coated may itself be at rest, with the application equipment or unit being moved. Alternatively the substrate to be coated, in particular a coil, may be moved, with the application unit at rest relative to the substrate or being moved appropriately.

Preference is given to employing spray application methods, such as compressed-air spraying, airless spraying, high-speed rotation, electrostatic spray application (ESTA), alone or in conjunction with hot spray application such as hot-air spraying, for example.

The applied coating compositions of the invention can be cured after a certain rest time. The rest time serves, for example, for the leveling and devolatilization of the coating films or for the evaporation of volatile constituents such as solvents. The rest time may be assisted and/or shortened by the application of elevated temperatures and/or by a reduced humidity, provided this does not entail any damage or alteration to the coating films, such as premature complete crosslinking, for instance.

The thermal curing of the coating compositions has no peculiarities in terms of method but instead takes place in accordance with the typical, known methods such as heating in a forced-air oven or irradiation with IR lamps. The thermal cure may also take place in stages. Another preferred curing method is that of curing with near infrared (NIR) radiation. The thermal cure takes place advantageously at a temperature of 30 to 200° C., more preferably 40 to 190° C., and in particular 50 to 180° C. for a time of 1 min up to 10 h, more preferably 2 min up to 5 h, and in particular 3 min to 3 h, although longer cure times may be employed in the case of the temperatures that are employed for automotive refinish, which are preferably between 30 and 90° C.

The coating compositions of the invention produce new cured coatings, especially coating systems, more particularly clearcoat systems; moldings, especially optical moldings; and self-supporting films, all of which are highly scratchproof and in particular are stable to chemicals and to weathering. The coatings and coating systems of the invention, especially the clearcoat systems, can in particular be produced even in film thicknesses>40 μm without stress cracks occurring.

For these reasons the coating compositions of the invention are of excellent suitability as decorative, protective and/or effect-imparting, highly scratchproof coatings and coating systems on bodies of means of transport (especially motor vehicles, such as motor cycles, buses, trucks or automobiles) or parts thereof; on buildings, both interior and exterior; on furniture, windows, and doors; on plastics moldings, especially CDs and windows; on small industrial parts, on coils, containers, and packaging; on white goods; on films; on optical, electrical, and mechanical components; and on hollow glassware and articles of everyday use.

The coating compositions and coating systems of the invention, especially the clearcoat systems, are employed in particular in the technologically and esthetically particularly demanding field of automotive OEM finishing and also of automotive refinish. With particular preference the coating compositions of the invention are used in multistage coating methods, particularly in methods where a pigmented basecoat film is first applied to an uncoated or precoated substrate and thereafter a film with the coating compositions of the invention is applied. Not only water-thinnable basecoat materials but also basecoat materials based on organic solvents can be used. Suitable basecoat materials are described for example in EP-A-0 692 007 and in the documents cited there in column 3 lines 50 et seq. The applied basecoat material is preferably first dried, i.e., at least some of the organic solvent and/or water is stripped from the basecoat film in an evaporation phase. Drying is accomplished preferably at temperatures from room temperature to 80° C. Drying is followed by the application of the coating composition of the invention. Subsequently the two-coat system is baked, preferably under conditions employed for automotive OEM finishing, at temperatures from 30 to 200° C., more preferably 40 to 190° C., and in particular 50 to 180° C., for a time of 1 min up to 10 h, more preferably 2 min up to 5 h, and in particular 3 min to 3 h, although longer cure times may also be employed at the temperatures employed for automotive refinish, which are preferably between 30 and 90° C.

The coats produced with the coating composition of the invention are notable in particular for an especially high chemical stability and weathering stability and also for a very good carwash resistance and scratchproofing, in particular for an excellent combination of scratchproofing and weathering stability with respect to UV radiation in a wet/dry cycle.

In a further preferred embodiment of the invention, the coating composition of the invention is used as a transparent clearcoat material for coating plastics substrates, especially transparent plastics substrates. In this case the coating compositions include UV absorbers, which in terms of amount and type are also designed for effective UV protection of the plastics substrate. Here as well, the coating compositions are notable for an outstanding combination of scratchproofing and weathering stability with respect to UV radiation in a wet/dry cycle. The plastics substrates thus coated are used preferably as a substitute for glass components in automobile construction, the plastics substrates being composed preferably of polymethyl methacrylate or polycarbonate.

Examples

Preparation of Inventive Component B

Preparation Example B1 Preparation of a Partly Silanized Polyisocyanate (HDI with 100 Mol % of IIIa: Conversion c=30 Mol %)

A three-neck glass flask equipped with a reflux condenser and a thermometer is charged with 57.3 parts by weight of trimerized hexamethylene diisocyanate (HDI) (Basonat HI 100 from BASF AG) and 88.0 parts by weight of solvent naphtha. With reflux cooling, nitrogen blanketing, and stirring, 21.8 parts by weight of N-[3-(trimethoxysilyl)propyl]butylamine (IIIa) (Dynasilan® 1189 from Degussa) are metered in at a rate such that 50 to 60° C. are not exceeded. After the end of the metered addition, the reaction temperature is held at 50 to 60° C. until the isocyanate mass fraction as determined by titration is at the theoretically calculated 70 mol %.

The solution of the partly silanized polyisocyanate has a solids content of 47.1% by weight.

Preparation Example B2 Preparation of a Partly Silanized Polyisocyanate (HDI with 70 Mol % of IIIa and 30 Mol % of IIa: Conversion c=30 Mol %)

A three-neck glass flask equipped with a reflux condenser and a thermometer is charged with 57.3 parts by weight of trimerized hexamethylene diisocyanate (HDI) (Basonat HI 100 from BASF AG) and 69.7 parts by weight of solvent naphtha. With reflux cooling, nitrogen blanketing, and stirring, a mixture of 14.8 parts by weight of N-[3-(trimethoxysilyl)propyl]butylamine (Dynasilan® 1189 from Degussa) (IIIa) and 9.2 parts by weight of bis[3-(trimethoxysilyl)propyl]amine (IIa) (Dynasilan® 1124 from Degussa) is metered in at a rate such that 50 to 60° C. are not exceeded. After the end of the metered addition, the reaction temperature is held at 50 to 60° C. until the isocyanate mass fraction as determined by titration is at the theoretically calculated 70 mol %.

The solution of the partly silanized polyisocyanate has a solids content of 53.9% by weight.

Preparation Example B3 Preparation of a Partly Silanized Polyisocyanate (HDI with 30 Mol % of IIIa and 70 Mol % of IIa: Conversion c=30 Mol %)

A three-neck glass flask equipped with a reflux condenser and a thermometer is charged with 57.3 parts by weight of trimerized hexamethylene diisocyanate (HDI) (Basonat HI 100 from BASF AG) and 69.7 parts by weight of solvent naphtha. With reflux cooling, nitrogen blanketing, and stirring, a mixture of 6.4 parts by weight of N-[3-(trimethoxysilyl)propyl]butylamine (Dynasilan® 1189 from Degussa) (IIIa) and 21.5 parts by weight of bis[3-(trimethoxysilyl)propyl]amine (IIa) (Dynasilan® 1124 from Degussa) is metered in at a rate such that 50 to 60° C. are not exceeded. After the end of the metered addition, the reaction temperature is held at 50 to 60° C. until the isocyanate mass fraction as determined by titration is at the theoretically calculated 70 mol %.

The solution of the partly silanized polyisocyanate has a solids content of 55.0% by weight.

Preparation Example B4 Preparation of a Partly Silanized Polyisocyanate (HDI with 100 Mol % of IIa: Conversion c=30 Mol %)

A three-neck glass flask equipped with a reflux condenser and a thermometer is charged with 57.3 parts by weight of trimerized hexamethylene diisocyanate (HDI) (Basonat HI 100 from BASF AG) and 88.0 parts by weight of solvent naphtha. With reflux cooling, nitrogen blanketing, and stirring, 30.7 parts by weight of bis[3-(trimethoxysilyl)propyl]amine (IIa) (Dynasilan® 1124 from Degussa) are metered in at a rate such that 50 to 60° C. are not exceeded. After the end of the metered addition, the reaction temperature is held at 50 to 60° C. until the isocyanate mass fraction as determined by titration is at the theoretically calculated 70 mol %.

The solution of the partly silanized polyisocyanate has a solids content of 63.0% by weight.

Preparation Example B5 Preparation of a Partly Silanized Polyisocyanate (HDI with 100 Mol % of IIIa: Conversion c=70 Mol %)

A three-neck glass flask equipped with a reflux condenser and a thermometer is charged with 57.3 parts by weight of trimerized hexamethylene diisocyanate (HDI) (Basonat HI 100 from BASF AG) and 88.0 parts by weight of solvent naphtha. With reflux cooling, nitrogen blanketing, and stirring, 49.4 parts by weight of N-[3-(trimethoxysilyl)propyl]butylamine (IIIa) (Dynasilan® 1189 from Degussa) are metered in at a rate such that 50 to 60° C. are not exceeded. After the end of the metered addition, the reaction temperature is held at 50 to 60° C. until the isocyanate mass fraction as determined by titration is at the theoretically calculated 30 mol %.

The solution of the partly silanized polyisocyanate has a solids content of 54.8% by weight.

Preparation Example B6 Preparation of a Partly Silanized Polyisocyanate (HDI with 70 Mol % of IIIa and 30 Mol % of IIa: Conversion c=70 Mol %)

A three-neck glass flask equipped with a reflux condenser and a thermometer is charged with 57.3 parts by weight of trimerized hexamethylene diisocyanate (HDI) (Basonat HI 100 from BASF AG) and 69.7 parts by weight of solvent naphtha. With reflux cooling, nitrogen blanketing, and stirring, a mixture of 34.6 parts by weight of N-[3-(trimethoxysilyl)propyl]butylamine (Dynasilan® 1189 from Degussa) (IIIa) and 21.5 parts by weight of bis[3-(trimethoxysilyl)propyl]amine (IIa) (Dynasilan® 1124 from Degussa) is metered in at a rate such that 50 to 60° C. are not exceeded. After the end of the metered addition, the reaction temperature is held at 50 to 60° C. until the isocyanate mass fraction as determined by titration is at the theoretically calculated 30 mol %.

The solution of the partly silanized polyisocyanate has a solids content of 61.9% by weight.

Preparation Example B7 Preparation of a Partly Silanized Polyisocyanate (HDI with 30 Mol % of IIIa and 70 Mol % of IIa: Conversion c=70 Mol %)

A three-neck glass flask equipped with a reflux condenser and a thermometer is charged with 57.3 parts by weight of trimerized hexamethylene diisocyanate (HDI) (Basonat HI 100 from BASF AG) and 88.0 parts by weight of solvent naphtha. With reflux cooling, nitrogen blanketing, and stirring, a mixture of 14.8 parts by weight of N-[3-(trimethoxysilyl)propyl]butylamine (Dynasilan® 1189 from Degussa) (IIIa) and 50.2 parts by weight of bis[3-(trimethoxysilyl)propyl]amine (IIa) (Dynasilan® 1124 from Degussa) is metered in at a rate such that 50 to 60° C. are not exceeded. After the end of the metered addition, the reaction temperature is held at 50 to 60° C. until the isocyanate mass fraction as determined by titration is at the theoretically calculated 70 mol %.

The solution of the partly silanized polyisocyanate has a solids content of 58.2% by weight.

Preparation of the Polyacrylate Polyol A

In a steel tank reactor equipped with monomer inlet, initiator inlet, thermometer, oil heating, and reflux condenser, 29.08 parts by weight of a commercial aromatic solvent mixture (Solventnaphtha® from DHC Solvent Chemie GmbH) are heated to 140° C. Then a mixture a1 of 3.39 parts by weight of solvent naphtha and 2.24 parts by weight of tert-butyl peroxy-2-ethylhexanoate is added with stirring, at a rate such that the addition of the mixture a1 is concluded after 6.75 h. 15 min after the beginning of the addition of the mixture a1, a mixture a2 consisting of 4.97 parts by weight of styrene, 16.91 parts by weight of tert-butyl acrylate, 19.89 parts by weight of 2-hydroxypropyl methacrylate, 7.45 parts by weight of n-butyl methacrylate, and 0.58 part by weight of acrylic acid is added at a rate such that the addition of the mixture a2 is concluded after 6 h. After the addition of the mixture a1, the reaction mixture is held at 140° C. for a further 2 h and then cooled to below 100° C. Subsequently the reaction mixture is diluted additionally with a mixture a3 of 3.70 parts by weight of 1-methoxyprop-2-yl acetate, 3.06 parts by weight of butyl glycol acetate, and 6.36 parts by weight of butyl acetate 98/100.

The resulting solution of the polyacrylate polyol A has a solids content of 52.4% (1 h, 130° C., forced-air oven), a viscosity of 3.6 dPas (ICI cone/plate viscometer, 23° C.), a hydroxyl number of 155 mg KOH/g, and an acid number of 10-13 mg KOH/g.

Formulation of the Coating Compositions

The coating compositions were formulated as follows:

Component 1, containing component A (polyol) and commercial additives and catalyst and solvent, is combined shortly before application with component 2, containing component B (modified polyisocyanate), and the components are stirred together until a homogeneous mixture is formed.

Application takes place pneumatically at 2.5 bar in three spray passes. Thereafter the coating is flashed off at room temperature for 5 minutes and subsequently baked at 140° C. for 22 minutes.

Table 1 lists all of the inventive coating compositions B1 to B7 in terms of the proportions of the components:

TABLE 1 Formulation of inventive coating compositions Example B1 B2 B3 B4 B5 B6 B7 Component B B1 B2 B3 B4 B5 B6 B7 Parts by weight of 45.0 45.0 45.0 45.0 45.0 45.0 45.0 polyacrylate polyol A of example Parts by weight of 52.0 47.2 48.3 43.7 144.9 133.0 153.0 component B Parts by weight of 2.1 2.2 2.3 2.4 6.9 7.2 7.8 catalyst¹ (Nacure 4167, King Industries) nonvolatile fraction 25% Parts by weight of BYK 0.2 0.2 0.2 0.2 0.2 0.2 0.2 301 (flow control agent, Byk Chemie) Parts by weight of 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Tinuvin 384.2 (Ciba) Parts by weight of 0.8 0.8 0.8 0.8 0.8 0.8 0.8 Tinuvin 292 (Ciba) Parts by weight of 20.0 20.0 20.0 20.0 20.0 20.0 20.0 Solventnaphtha (DHC Solvent Chemie GmbH) Equivalent ratio of free 1.00:1.00 1.00:1.00 1.00:1.00 1.00:1.00 1.00:1.00 1.00:1.00 1.00:1.00 isocyanate groups in component B to hydroxyl groups in polyacrylate polyol A Si content in % by 1.5 1.8 2.5 2.9 3.9 4.5 5.9 mass²) ¹catalyst based on amine-blocked phosphoric acid partial ester ²)Si content calculated from the amounts of (IIa)/(IIIa) employed, based on the solids content of the coating compositions

The storage moduli E′(200) and E′(min) and also the glass transition temperature Tg of the respective cured coating are measured by dynamic-mechanical thermo-analysis (DMTA) at a heating rate of 2 K/min using the DMTA V instrument from Rheometrics Scientific at a frequency of 1 Hz and an amplitude of 0.2%. The DMTA measurements are carried out on free films with a thickness of 40 μm±10 μm. For this purpose the coating composition under test is applied to substrates to which the coating obtained does not adhere. Examples of suitable substrates include glass, Teflon, polyethylene terephthalate and polypropylene. The resulting coating is cured for 20 minutes at an article temperature of 140° C. and is stored at 25° C. for 8 days after curing, before the DMTA measurements are carried out.

The scratchproofing of the surfaces of the resultant coatings was tested by means of the Crockmeter test (in general in accordance with EN ISO 105-X12, with 10 double rubs and an applied force of 9 N, using 9 μm abrasive paper (3M 281Q, using wetordry™production™), with subsequent determination of the residual gloss at 20° using a commercially customary gloss meter), and by means of the hammer test (10 or 100 double rubs with steel wool (RAKSO®00(fine)) with an applied weight of 1 kg, implemented with a hammer. Subsequently, again, the residual gloss at 20° is determined with a commercially customary gloss meter) and the weathering stability is investigated by means of the CAM180 test (to DIN EN ISO 11341 February 98 and DIN EN ISO 4892-2 November 00). The results are listed in Table 2.

TABLE 2 Properties of the clearcoat films produced with the inventive coating compositions Example B1 B2 B3 B4 B5 B6 B7 E′ (200° C.) in Pa 2.74 * 10⁷ 3.58 * 10⁷ 3.27 * 10⁷ 6.73 * 10⁷ 5.94 * 10⁷ 1.68 * 10⁸ 2.99 * 10⁸ E′ (min) in Pa 2.36 * 10⁷ 3.23 * 10⁷ 2.99 * 10⁷ 5.47 * 10⁷ 5.33 * 10⁷ 1.01 * 10⁸ 1.85 * 10⁸ Post-crosslinking 1.2 1.1 1.1 1.2 1.1 1.7 1.6 index PCI Crockmeter test 41 53 58 63 75 88 95 (residual gloss in %) Hammer test 10 DR 38 49 60 64 79 88 93 (residual gloss in %) Hammer test 100 DR 0 1 18 28 65 81 92 (residual gloss in %) Gloss 82 85 85 85 86 86 86 CAM 180 test (h) 5500 5250 5000 4500 5250 5000 4000 until appearance of cracks

Table 2 shows the properties of the coatings of examples B1 to B7, prepared from the inventive coating compositions comprising an isocyanurate adduct B originating from the reaction of the HDI isocyanurate with, in each case, a mixture of a component IIa and a component IIIa (Examples B2, B3, B6 and B7), in comparison to coating compositions comprising an isocyanurate adduct B originating from the reaction with the HDI isocyanurate, referred to as HDI for short below, and exclusively one component IIa (example B4) or IIIa (examples B1 and B5).

In all of examples B1 to B7, coatings with the low degrees of post-crosslinking, in accordance with the invention, and the corresponding good scratch resistance and weathering resistance properties are obtained. It is noted first of all that, generally speaking, the smaller the fraction of the silane crosslinking as a proportion of the crosslinking overall, the lower the post-crosslinking in general and hence the smaller the post-crosslinking index (PCI). For instance, in the case of examples B1 and B2, with a very low proportion of silane crosslinking (conversion of the isocyanate groups of the HDI of 30 mol % and high fraction of monofunctional silane structural units of 100 mol % structural units III in example B1 and 70 mol % structural units III in example B2) lower degrees of post-crosslinking are obtained than in example 7, with a high proportion of silane crosslinking (conversion of the isocyanate groups of the HDI of 70 mol % and high fraction of difunctional silane structural units of 70 mol % structural units II in example B7). At the same time, however, as the fraction of silane crosslinking goes down, there is also a decrease in the scratch resistance, with the consequence that, in order to achieve very high scratchproofing values, relative high fractions of silane crosslinking are desired, as is likewise shown by a comparison of examples B1 and B2 with B7.

With a conversion of the isocyanate groups of the HDI of 30 mol %, B1 (containing only structural units III) as against B4 (containing only structural units II), exhibit a much longer time in the CAM180 test until cracks appear. Correspondingly, for a degree of conversion of the isocyanate groups of the HDI of 70 mol %, example B5 (containing only structural units III) as against B7 (containing 70 mol % structural units II) exhibits a significantly longer time in the CAM 180 test before the appearance of cracks. The situation with the scratchproofing is the inverse of this: with a conversion of the isocyanate groups of the HDI of 30 mol %, B1 (containing only structural units III) as against B4 (containing only structural units II), exhibit a much weaker scratchproofing in the various scratch tests. Correspondingly, for a conversion of the isocyanate groups of the HDI of 70 mol %, example B5 (containing only structural units III) as against to B7 (containing 70 mol % structural units II) shows a significantly weaker scratchproofing in the various scratch tests. Since the relative fraction of the structure II hence shows itself to be responsible for the scratchproofing, and the fraction of the structure III for the weathering resistance, a careful blending of the amounts used of both siloxane amines IIa and IIIa allows a fine-tuned balance to be struck between weathering time and scratchproofing.

By way of example, B1 and B4 may be contrasted with B2 and B3 in the group with 30 mol % conversion of the isocyanate functions. B1 achieves high weathering values, but the scratchproofing is moderate. B4 has good scratchproofing values, but is weaker in weathering. Both examples B2 and B3 have better scratchproofing than B1 and better weathering times than B4.

Similar comments apply to B5 contrasted with B6 and B7 in the group with 70 mol % conversion of isocyanate, although here both scratchproofing and weathering resistance are influenced more strongly, as a result of the high relative fraction of the siloxane functions. In addition it is clear that, with a high conversion of the isocyanate functions, the relative fraction of the structure III influences the weathering resistance significantly more strongly than structure II influences the scratchproofing, as can easily be seen from comparing the values of B6 and B7. In general, the scratchproofing value correlates with the conversion of the isocyanate groups with the compounds II and III, and in this context a higher conversion of the isocyanate groups is also necessary for the attainment of very high scratchproofing.

Comparative Examples 1 to 7

Examples 1 to 7 were repeated, albeit with the sole difference that this time, instead of the catalyst based on amine-blocked phosphoric acid partial esters, blocked para-toluenesulfonic acid was used as the catalyst.

Table 3 lists all of the coating compositions of the comparative examples, in terms of the proportions of the components:

TABLE 3 Formulation of the coating compositions of the comparative examples Example VB1 VB2 VB3 VB4 VB5 VB6 VB7 Components B B1 B2 B3 B4 B5 B6 B7 Parts by weight of 45.0 45.0 45.0 45.0 45.0 45.0 45.0 polyacrylate polyol A of example Parts by weight of 52.0 47.2 48.3 43.7 144.9 133.0 153.0 component B Parts by weight of 1.1 1.1 1.2 1.2 3.5 3.6 3.9 catalyst³ (Dynapol 1203, Degussa), nonvolatile fraction 50% Parts by weight of BYK 0.2 0.2 0.2 0.2 0.2 0.2 0.2 301 (flow control agent, Byk Chemie) Parts by weight of 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Tinuvin 384.2 (Ciba) Parts by weight of 0.8 0.8 0.8 0.8 0.8 0.8 0.8 Tinuvin 292 (Ciba) Parts by weight of 20.0 20.0 20.0 20.0 20.0 20.0 20.0 Solventnaphtha (DHC Solvent Chemie GmbH) Equivalent ratio of free 1.00:1.00 1.00:1.00 1.00:1.00 1.00:1.00 1.00:1.00 1.00:1.00 1.00:1.00 isocyanate groups in component B to hydroxyl groups in polyacrylate polyol A Si content in % by 1.5 1.8 2.5 2.9 3.9 4.5 5.9 mass⁴) ³catalyst based on blocked p-toluenesulfonic acid ⁴)Si content calculated from the amounts of (IIa)/(IIIa) employed, based on the solids content of the coating compositions

TABLE 4 Properties of the clearcoat films produced with the coating compositions of the comparative examples Example VB1 VB2 VB3 VB4 VB5 VB6 VB7 E′ (200° C.) in Pa 3.08 * 10⁷ 4.13 * 10⁷ 4.05 * 10⁷ 7.39 * 10⁷ 6.03 * 10⁷ 1.80 * 10⁸ 2.79 * 10⁸ E′ (min) in Pa 1.08 * 10⁷ 1.13 * 10⁷ 0.99 * 10⁷ 1.54 * 10⁷ 1.73 * 10⁷ 3.39 * 10⁷ 4.23 * 10⁷ Post-crosslinking 2.9 3.6 4.1 4.8 3.5 5.3 6.6 index PCI Crockmeter test 14 6 7 13 35 56 78 (residual gloss in %) Hammer test 10 DR 16 23 32 36 44 67 79 (residual gloss in %) Hammer test 100 DR 0 0 0 7 20 53 58 (residual gloss in %) Gloss 82 85 84 84 84 85 85

The comparison of the inventive examples 1 to 7 with the comparative examples VB1 to VB7 shows that the inventive coatings of examples B1 to B7 exhibit good scratchproofing directly after final curing, whereas the corresponding coatings of the comparative examples VB1 to VB7, with a high post-crosslinking index PCI>2, all exhibit a significantly poorer scratchproofing after the final 20-minute 140° C. cure. More particularly, therefore, the coatings of comparative examples VB1 to VB4, with a low degree of silanization, must be given an additional thermal aftertreatment following the cure, in order to obtain the good scratchproofing that is required in the field of OEM finishing; to do so, however, is very costly and inconvenient and therefore impracticable. Without this aftertreatment, owing to the low scratchproofing, the coatings can be handled to a limited extent at best, given the risk of damage. Even the polishability of the resulting coatings, as is required for line refinishing, is present only conditionally for the coatings of the comparative examples.

As the silane content goes up, the inventive coatings, more particularly those of examples B3 to B7, also exhibit a better gloss than the coatings of the corresponding comparative examples.

Furthermore, as the degree of silanization goes up and the proportion of difunctional silane (IIa) goes up, in other words from B1 to B7 and from VB1 to VB7, the effect of the catalyst on the post-crosslinking index becomes increasingly great. At a low degree of silanization, with 30 mol % degree of conversion of the isocyanate groups, the inventive example B1, using the high-activity catalyst based on the amine-blocked phosphoric acid partial ester, exhibits a PCI of 1.1, whereas the corresponding comparative example, using the corresponding amount of the substantially less effective catalyst based on blocked p-toluenesulfonic acid, has an excessively high PCI of 2.9. Owing to this excessively high PCI, the coating of comparative example VB1 has the aforementioned completely inadequate scratchproofing. As the amount of silane increases in series via VB2, VB3, up to VB7, the post-crosslinking index, PCI, of the comparative examples, and hence the post-crosslinking, increases drastically to reach a PCI value of 6.6 in the case of a high degree of silanization, with 70 mol % degree of conversion of the isocyanate groups, in comparative example VB7, in comparison to the only slightly increased post-crosslinking index of PCI=1.6 in the corresponding inventive example B7. Post-crosslinking, however, proceeds in a less controlled manner than curing during the thermal treatment, and the final hardness of the resulting coatings after post-crosslinking has taken place is very much more difficult to set, if indeed it can be set at all. This leads, in general, to properties of poor reproducibility in the resultant coatings. Above all, however, the comparative examples, with high to very high post-crosslinking, as in comparative examples VB6 and VB7, exhibit a very high risk of the occurrence of stress cracks, so making them unsuitable for the demanding sector of automotive OEM finishing. 

1. A coating composition comprising (a) at least one hydroxyl-containing compound (A), (b) at least one compound (B) having free and/or blocked isocyanate groups, and (c) at least one catalyst (D) for the crosslinking of silane groups, wherein (i) one or more constituents of the coating composition contain hydrolyzable silane groups, (ii) the coating composition can be finally cured to a coating which has statistically distributed regions of an Si—O—Si network, and the finally cured coating obtained from the coating composition has a post-crosslinking index (PCI) of less than 2, where the post-crosslinking index (PCI) is defined as the ratio of the storage modulus E′(200) of the finally cured coating, measured at 200° C., to the minimum of the storage modulus E′(min) of the finally cured coating, measured at a temperature above the measured glass transition temperature Tg, the storage moduli E′(200), E′(min), and the glass transition temperature Tg are measured on free films with a thickness of 40 μm±10 μm by dynamic-mechanical thermo-analysis (DMTA) at a heating rate of 2 K per minute and at a frequency of 1 Hz, and the DMTA measurements on free films with a thickness of 40 μm±10 μm which have been cured for 20 minutes at an article temperature of 140° C. and stored at 25° C. for 8 days after curing.
 2. The coating composition of claim 1, wherein the finally cured coating obtained from the coating composition has a post-crosslinking index (PCI) of less than or equal to 1.8.
 3. The coating composition of claim 1, wherein the catalyst (D) comprises phosphorus.
 4. The coating composition of claim 3, wherein the catalyst (D) is selected from the group of substituted phosphoric monoesters, substituted phosphoric diesters, the corresponding amine-blocked phosphoric esters, and mixtures thereof.
 5. The coating composition of claim 4, wherein the catalyst (D) is blocked with a tertiary amine.
 6. The coating composition of claim 4, wherein the catalyst (D) is selected from the group of amine-blocked phosphoric acid ethylhexyl partial esters and amine-blocked phosphoric acid phenyl partial esters.
 7. The coating composition of claim 1, wherein the finally cured coating obtained from the coating composition has a storage modulus E′(200), measured at 200° C., of less than 4*10⁸ Pa.
 8. The coating composition of claim 1, wherein one or more constituents of the coating composition comprise at least partly one or more identical or different structural units of the formula (I) —X—Si—R″_(x)G_(3-x)   (I) where G=identical or different hydrolyzable groups, X=organic radical, R″=alkyl, cycloalkyl, aryl or aralkyl, it being possible for the carbon chain to be interrupted by nonadjacent oxygen, sulfur or NRa groups, with Ra=alkyl, cycloalkyl, aryl or aralkyl, x=0 to
 2. 9. The coating composition of claim 1, wherein one or more constituents of the coating composition comprise between 2.5 and 97.5 mol %, based on the entirety of structural units (II) and (III), of at least one structural unit of the formula (II) —N(X—SiR″_(x)(OR′)_(3-x))_(n)(X′—SiR″_(y)(OR′)_(3-y))_(m)   (II) where R′=hydrogen, alkyl or cycloalkyl, it being possible for the carbon chain to be interrupted by nonadjacent oxygen, sulfur or NRa groups, with Ra=alkyl, cycloalkyl, aryl or aralkyl, X,X′=linear and/or branched alkylene or cycloalkylene radical having 1 to 20 carbon atoms, R″=alkyl, cycloalkyl, aryl or aralkyl, it being possible for the carbon chain to be interrupted by nonadjacent oxygen, sulfur or NRa groups, with Ra=alkyl, cycloalkyl, aryl or aralkyl, n=0 to 2, m=0 to 2, m+n=2, x=0 to 2, and y=0 to 2, and between 2.5 and 97.5 mol %, based on the entirety of structural units (II) and (III), of at least one structural unit of the formula (III) -Z-(X—SiR″_(x)(OR′)_(3-x))   (III), where Z=-NH—, —NR—, —O—, with R=alkyl, cycloalkyl, aryl or aralkyl, it being possible for the carbon chain to be interrupted by nonadjacent oxygen, sulfur or NRa groups, with Ra=alkyl, cycloalkyl, aryl or aralkyl, x=0 to 2, and X, R′, R″ have the meaning given in formula (II).
 10. The coating composition of claim 9, wherein one or more constituents of the coating composition contain between 5 and 95 mol %, based in each case on the entirety of the structural units (II) and (III), of at least one structural unit of the formula (II), and between 5 and 95 mol %, based in each case on the entirety of the structural units (II) and (III), of at least one structural unit of the formula (III).
 11. The coating composition of claim 9, wherein the structural elements (II) and (III) are present in fractions of 2.5 to 97.5 mol %, in each case based on the sum of the functional groups critical for crosslinking in the coating composition, formed from the fractions of the hydroxyl and isocyanate groups and from the fractions of the structural elements (II) and (III).
 12. The coating composition of claim 8, wherein the polyisocyanate (B) comprises the respective structural units (I) or (II) or (III).
 13. The coating composition of claim 12, wherein, in the polyisocyanate (B), between 2.5 and 90 mol % of the isocyanate groups in the core polyisocyanate structure have undergone reaction to structural units (II) and between 2.5 and 90 mol % of the isocyanate groups in the core polyisocyanate structure have undergone reaction to structural units (III) and/or the total fraction of the isocyanate groups in the core polyisocyanate structure that have undergone reaction to structural units (II) and/or (III) is between 5 and 95 mol %.
 14. The coating composition of claim 12, wherein the core polyisocyanate structure is selected from the group of 1,6-hexamethylene diisocyanate, isophorone diisocyanate, and 4,4′-methylenedicyclohexyl diisocyanate, the biuret dimers of the aforementioned polyisocyanates, the isocyanurate trimers of the aforementioned polyisocyanates, and mixtures thereof.
 15. The coating composition of claim 1, wherein the polyol (A) comprises at least one poly(meth)acrylate polyol.
 16. A multistage coating method which comprises applying a pigmented basecoat film to an uncoated or precoated substrate and thereafter applying a film of the coating composition of claim
 1. 17. The multistage coating method of claim 16, wherein, following the application of the pigmented basecoat film, the applied basecoat material is first dried at temperatures from room temperature to 80° C. and, following the application of the coating composition of claim 1, the system is cured at temperatures from 30 to 200° C. for a time of 1 min up to 10 h.
 18. The coating composition of claim 1 that is a clearcoat material for automotive OEM finishing or automotive refinish.
 19. The coating composition of claim 2, wherein the finally cured coating obtained from the coating composition has a post-crosslinking index (PCI) of less than or equal to 1.5.
 20. The coating composition of claim 7, wherein the finally cured coating obtained from the coating composition has a storage modulus E′(200), measured at 200° C., of less than or equal to 3*10⁸ Pa. 